Draft hood



L. N. HUNTER Feb. 8, 1936.

DRAFT HOOD Filed April 17, 1933 2 Sheets-Sheet l INVENTOR Feb; 13, 193%.g HUNTEQ {2,Q3L314 DRAFT HOOD Filed April 17, 1933 2 Sheos-Sheet 2INVENTOR ($.44 n. M

W PM "W Patented Feb. 18, 1936 UNITED STATES PATENT OFFICE DRAFT HOODApplication April 17, 1933, Serial No. 666,500

2 Claims.

This invention relates to what are known as draft hoods or draftdiverters for fuel burning appliances, such as gas-fired heatingfurnaces and boilers.

A well constructed gas burning appliance is designed to operate With anextremely low or practically negligible chimney draft. At the same timeit should be connected with a chimmy in order that the products ofcombustion can be properly disposed of. The draft hood or draft diverteris located in the flue passage between the appliance and the chimney,and its main function is to break the chimney draft through theprovision of passages which open into the room so that air may be drawnfrom the room into the chimney without having to pass through the gasburning appliance, allowing the appliance to operate under practicallyno draft. If this relief were not provided, too much air would besupplied to the appliance, with the result that its efiiciency would beimpaired and there would be danger of the strong draft extinguishing theflames in the pilot burners or in the main burners if they were'verylow.

With so little draft the possibility of downdraft or back-draft isgreater, and a second important function of the draft diverter is toprotect the gas appliance when there is a downdraft or a back-draft. Ifthere is a down-draft or back-draft and the draft diverter does notfunction properly, the gases of combustion do not escape from thecombustion chamber with sufficient rapidity, causing the flames tofloat, and there is incomplete combustion and the possibility of theflame being smothered out. In the caseof incomplete combustion, carbonmonoxide is generated.

A well designed draft hood should therefore: effectively'breakthechimney'draft; the relief openings should be so disposed that the aircoming in through the relief openings from the surrounding' atmospheredoes not create a suction on the flue passage from the appliance and itshould provide for the discharge of the products of combustion throughthe relief openings at an ample rate to insure proper combustion in thecombustion chamber in the event that the chimney becomes entirelystopped up or in the event that there is a down-draft or back-draft.Moreover, it should be such that under normal conditions all of theproducts of combustion pass up the chimney and do not escape through therelief openings into the atmosphere. Another important function is thatit shall prevent back-drafts into the appliance sufiicient to blow theflames, particularly the small flames of pilot burners.

Draft diverters as heretofore constructed have been sufficient to takecare of one or more of these requirements, but I am aware of no draftdiverter which adequately fulfills all of the requirements because thesecuring of one function with previous types of draft diverters has beenaccomplished only with the impairment of another factor. 10

According to the present invention there is provided a draft diverterwhich has adequate relief openings for breaking the draft wherein theseopenings are so disposed and arranged that the incoming air does nothave any effect on the gases discharging from the appliance. It is soconstructed that it will adequately handle all of the products ofcombustion of the appliance under what are termed neutral draftconditions by the American Gas Association. By this it is meant thatwith practically no draft in the chimney, but with the chimney open, allof the gases of combustion from the appliance will pass up the chimneywithout spilling out through the relief openings into the surroundingatmosphere. 2 This is determined by smoke tests arranged undercontrolled conditions. If in these smoke tests it appears that the smokecomes out the relief openings, the diverter is not capable of takingcare of the products of combustion under neutral draft conditions.

The diverter is further so constructed that in the event of a back-draftit will prevent the flames from being blown out or smothered and in caseof the flue being completely closed, the 5 products of combustion willdischarge through the relief openings without building up a backpressure in the combustion chamber sufficient to impair combustion to apoint where the concentration of carbon monoxide in an air-free sam- 40ple of the products of combustion does not exceed 0.04%, this being themaximum carbon monoxide concentration permitted by the American GasAssociation requirements for househeating appliances.

The invention may be readily understood by reference to the accompanyingdrawings, in which,

Figure 1 illustrates a transverse vertical section through the upperportion of a gas burning 5o appliance and through a draft hoodconstructed in accordance with my invention;

Figure 2 is a top plan view of Fig. 1;

Figure 3 is a View similar to Fig. 1 showing a preferred construction ofthe hood for the larger sizes of boilers Where a plurality of flueoutlets are desirable; and

Figure 4 is a view similar to Fig. 2 showing a top plan view of thearrangement illustrated in Fig. 3.

In the drawings, 2 designates the chamber in the upper part of agas-fired boiler, the gases of combustion from the burners (not shown)rising through the spaces 3 between-the boiler sections 4 into the space2. The space 2 is covered by a flue top 5, this flue top having adischarge opening 6 therein, the opening 6 being surrounded by a flange"I that projects through the top cover 8 of the boiler. Placed aroundthe flange l in order to provide slightly increased height is a collar 9to which is secured a plurality of supporting arms 10, which arms support an inverted conical bafile or deflector I l the baffle II beingcentrally supported by the arms In over the flue opening 6. The baffle,moreover, is preferably of less diameter than the flue opening 6.

Supported on the top of the boiler is a hood l2, which is shown as beingsquare, but which can be of any suitable contour, and which has a widthconsiderably larger than the diameter of the ring 9 so that the verticalwalls 12a of this hood are spaced a considerable distance away from thedraft discharge ring 9. The side walls [2a of the hood are provided witha series of draft relief openings l2b, these relief openings beingformed of the side walls of the hood and covering the major portion ofthe area of the side walls.

The top of the hood l2 has a circular opening I3 therethrough, thisopening being surrounded by a vertical flange M. The vertical flange l4serves to center a circular dome l5 above the hood, the dome l5 being ofa height substantially equal to the height of the hood. The dome has acircular opening l6 therein with a flange l1 thereabout over which isfitted the flue pipe l8. The opening I6 is in vertical alinement withthe opening 6. The dome and hood together form a collector unit, and theeffective lower edge of this collector unit is the top of the reliefopenings in the hood. The open area provided by the relief openings isthe equivalent to having the hood open completely below the plane of thetop of the relief openings so that for all purposes the effectivelowermost edge of the hood is the plane of the tops of the reliefopenings.

The purpose of the different parts of the construction may now befollowed. Assume first that the flue pipe I8 is connected to the chimneyin which there is normally a strong draft. The gases of combustionpassing through the opening 6 enter the hood and dome and pass out theflue pipe l8. The force of the draft, however, is broken by the reliefopenings |2b so that this draft is not communicated to the interior ofthe boiler. By reason of the large dimension of the hood and the largeamount of open area in the side walls thereof, the velocity of theincoming air through any one opening is relatively small so that the airdoes not sweep across the top of the ring 3 in such manner as to haveany suction effect. The distance from the opening IE to the draft baifieII is so great that the air coming in through the relief openings canreach the flue pipe without producing any low pressure area directlyabove the opening 6, tending to accelerate the flow of gases out of thechamber 2. Moreover, the greater portion of the open area provided bythe relief openings is above the top of the ring 9, serving further toproduce a condition in which the incoming air produces no suction effectin the opening 6. The area of the hood and the diameter of the dome,moreover, is such that if the draft is not strong the gases dischargingfrom the furnace can expand and spread out, and then travel out the fluepipe l8, but they will not spill through the relief openings lZb.However, if there is a back-draft in the pipe H3 or the flue becomesentirely choked, the gases of combustion can fill the dome l5 and thenflow out through the relief openings I21) and no substantial backpressure will be built up in the chamber 2, because of the fact that therelief openings are largely above the top of the ring 9, so that theflow of gases is generally upward and outward. If the dome l5 were notprovided and the hood l2 were brought in to the diameter of the pipe IS,the spent gases would have a greater choking effect on the escape of thegases of combustion from the opening 6 and therefore the dome l5materially improves the action of the hood in the event of the chimneyor flue I8 being blocked. The large area of the relief openings inproportion to the area of the flue gas outlet 6 also facilitates theremoval of the spent gases when the flue I8 is blocked or underconditions of back-draft.

In the event of a current of air coming down the chimney and pipe I8,the dome I5 permits the air to expand before it reaches the draftdeflector l and the back flow of air can escape through the reliefopenings l2b without exerting any appreciable back pressure on the flueopenings 6. The draft baffle of course breaks any direct down flow ofair that may occur.

Moreover, since the dome l and the hood I! provide progressively largerchambers into which the back-draft can expand, the draft baffle I I canbe relatively small in diameter. Being relatively small in diameter, itoffers a minimum impedance to the flow of the burnt gases under normaloperating conditions.

Moreover, the draft relief openings 121) being in the side walls of thehood and being of such extensive area, they are not likely to becomeclosed or stopped up sufficiently to impair their function, whereas withthe usual type of conical hood wherein the draft relief space is in thebottom, the edge of the hood may be so close to the top of the furnacethat the space may become choked or restricted to an undesirable extent.

In boilers of the larger sizes it is desirable to provide a plurality offlue outlet openings, and the preferred manner of constructing the drafthood for boilers having a plurality of outlets is shown in themodification illustrated in Figs. 3 and 4. In these views the boiler,designated generally as has a flue top 2| therein similar to the fluetop 5 of Figure 1, except that this flue top spans a greater number ofboiler sections and is provided with a plurality of discharge outlets 22instead of a single one, as shown in Figure 1. I have shown a flue topin which there are two discharge outlets, but this number can beincreased as the number of boiler sections is increased. Surroundingeach flue outlet 22 is a ring 23 having arms 24 supporting the invertedcone 25 similar to the cone H of Figure 1. Formed on top of the boilerhousing is a single large hood 26 which, in the example shown, isrectangular and which has a length and width such that the side walls26a thereof are spaced a considerable distance away from the flueoutlets 22. The distance of the side walls 26a from the outlets 22 ispreferably as much as the diameter of the flue outlets 22.

The side walls 26a are perforated throughout the greater portion oftheir area so as to provide an ample number of draft relief openings.This hood 26 has a plurality of outlets 21, there being one outlet 21over each outlet 22, and each outlet 21 is provided with a dome 28. Thedomes 28 have restricted upper portions 29 providing for a flue pipe,connection.

The hood as thus constructed gives the same advantages as the oneillustrated in Figs. 1 and 2, and has the additional advantage ofproviding a single hood for a boiler requiring two or more fluedischarge outlets.

While this invention has been described particularly in connection Withgas burning appliances, it is also adapted for use with various otherfuels.

Not only does the hood function well under all possible chimneyconditions, but it is of a unique and pleasing appearance.

Various changes and modifications may be made in the particularconstruction and arrangement of parts and obviously where desired thehood l2 and dome l5 may be in one piece, all within the contemplation ofmy invention and under the scope of the following claims.

I claim:

1. A draft hood comprising a collector unit having a fiue connection atthe top thereof, an opening to atmosphere around its eifective loweredge, said collector being of downwardly increasing diameter, meansbelow the eifective lower edge of the collector for discharging gases ofcombustion into the collector, and a back draft bafile over said lastmeans having a diameter less than the diameter of said means and havingits upper edge in a plane below the lowermost edge of said collector.

2. A draft hood comprising a collector unit having a flue connection atthe top thereof, an opening to atmosphere around its effective loweredge, said collector being of downwardly increasing diameter, meansbelow the effective lower edge of the collector for discharging gases ofcombustion into the collector, and a back draft baflie over said lastmeans having a diameter less than the diameter of said means and havingits upper edge in a plane below the lowermost edge of said collector,the collector comprising a dome portion and a hood portion below thedome portion, there being a shoulder between the lowermost edge of thedome portion and the effective lower edge of the hood, said means fordischarging gases into the collector being of less diameter than thelower edge of the dome portion.

LOUIS N. HUNTER.

